Sense Number 3: (cause to) become less intense or strict

Examples:
The government relaxed the curfew after most of the rebels were caught.
The rules relaxed after the new director arrived.
After several hours of intense concentration, she relaxed her efforts.
Don't relax your guard just because this last outbreak did not become an epidemic.
He relaxed his attention for just a moment, and she slipped away.
The committee relaxed the definition of "associate member" at the last meeting.